DE69300304T2 - Coverable, heat-curable solutions made from a prepolymer binder modified with reactive thinner. - Google Patents

Description

The present invention relates to abrasives that use a binder that attaches abrasive grains to a backing layer, to fibers of a fibrous mat, or to a molded mass, and to methods for making the abrasives using a binder prepolymer solution containing a reactive diluent.

Abrasives can be classified as coated, bonded and nonwoven. Coated abrasives generally comprise a flexible backing having applied thereto an abrasive coating comprising abrasive grains and a binder. The backing can be selected from paper, cloth, foil, vulcanized fiber, etc., or a combination of one or more of these materials or refined versions thereof. The abrasive grains can be made from flint, garnet, alumina, alumina-zirconia, ceramic alumina, diamond, silicon carbide, etc. The binders generally comprise hardened variations of hide glue or varnish or one or more resins, e.g., phenolic, urea-formaldehyde, melamine-formaldehyde, urethane, epoxy and acrylic resins. Phenolic resins include phenol-aldehyde type resins.

Nonwoven abrasives typically comprise a fibrous mat of fibers having an abrasive coating on at least a portion of its surface comprising abrasive grains and a binder. The fibers may be made from various polymers including polyamides, polyesters, polypropylene, polyethylene and various copolymers. Naturally occurring fibers such as cotton, wool, bast fibers and various animal hairs may also be suitable.

For coated and nonwoven abrasives, a "coating" of a binder prepolymer solution including one or more of the above-mentioned resins may be used, both to attach the abrasive grains to the backing when the resin is cured and to align the abrasive grains on the backing or across the raised fibrous mat. A "size coating" of a resinous binder material may be applied over the coating and the abrasive grains, firmly bonding the abrasive grains to the backing or fibrous mat. The resin of the glue coating can be the same as that used to form the coating or a different material.

In the manufacture of coated and nonwoven abrasives, the coating and abrasive grains are usually first applied to the backing or raised fibrous mats, the coating is partially cured, then the size coating is applied, and finally the coating and size coating are fully cured.

In general, binders that include thermally cured resins provide abrasives that have excellent properties such as heat resistance. To render the resin prepolymers coatable, to obtain the appropriate coating viscosities, and to obtain defect-free coatings, a solvent is usually added to the uncured resins.

When polyester or cellulose backings or raised fibrous mats of these fibers are used, the curing temperature is sometimes limited to 130ºC. At this temperature, the long curing time together with solvent removal requires the use of confined cured areas. Disadvantages of confined cured areas include the emission of volatile organic compounds (VOCs) such as organic solvents, unreacted resin prepolymers such as phenol and formaldehyde, and the like.

Among the many thermally curable resins, including phenolic resins, urea-aldehyde resins, urethane resins, melamine resins, epoxy resins and alkyl resins, phenolic resins are widely used to make abrasives because of their thermal properties, availability, low cost and ease of handling. Although phenolic resins are discussed here, it will be apparent to those skilled in the art that the characteristics discussed here are applicable to other thermally curable resins such as those mentioned above. The monomers currently used most extensively to make phenolic resins are phenol and formaldehyde. Other important phenolic starting materials are the alkyl-substituted phenols, including cresols, xylenols, p-tert-butylphenol, p-phenylphenol and nonylphenol. Diphenols, e.g. resorcinol (1,3-benzenediol) and bisphenol-A (bis-A or 2,2-bis(4-hydroxyphenyl)propane) are used to a lesser extent for applications that require special properties.

There are two different basic types of phenolic resins: phenolic resole and novolak resins. The increase in molecular weight and curing of phenolic resole resins are catalyzed by alkaline catalysts. The molar ratio of aldehyde to phenolic component is greater than or equal to 1.0, typically between 1.0 and 3.0. In the manufacture of adhesive coatings for Nonwoven and coated abrasives have a standard phenolic resin feedstock composition of 70% solids of the condensate of a 1.96:1.0 formaldehyde:phenol mixture to which 2% potassium hydroxide, based on the weight of the phenol, is added as a catalyst. The phenolic resin composition typically has 25-28% water and 3-5% propylene glycol ether, which are necessary to reduce the viscosity of the resin. Before the resin is used as a component of a coating or size coat, i.e. to make it coatable, further reduction in viscosity is often achieved through the use of VOC. A binder prepolymer solution containing a phenolic resin used to make a coating may contain up to 40% of a VOC, e.g. isopropyl alcohol, which reduces viscosity and makes the phenolic resin compatible with the resin modifiers (plasticizers), while a binder prepolymer solution used to make a size coating may contain up to 20% of a VOC, e.g. diethylene glycol ethyl ether. Unreacted phenol and formaldehyde also contribute to VOCs in the final, cured resin.

In order to reduce VOC emissions, attempts have been made to increase the water compatibility of phenolic resins. Fisher describes in an unsourced review article entitled "Water Compatible Phenolic Resins" in Proceedings of the American Chemical Societv. Division of Polymeric Material: Science and Engineering; 65 pp. 275-276 (1991) currently known processes for producing "water compatible" phenolic resins, their advantages and their disadvantages.

Unfortunately, the water tolerance of phenolic resins suffers in many formulations designed to reduce VOCs. "Water tolerance" refers to measuring the maximum amount of distilled water in weight percent, based on the initial weight of resin, that can be added to a stirred, uncured phenolic resin by titrating until a visually visible phase separation (detected by a milky appearance) of the resin/water mixture into an aqueous and an organic phase begins. As mentioned by Hoy et al. (see below), it is essential that during the drying phase after a particular substrate has been coated with a coating, a single phase is maintained until the water has evaporated, leaving the insoluble residue of the organic polymer. Another problem with many water compatible phenolic resins is that the gel time is increased. The term "gel time" as used herein refers to the length of time at a given temperature in which a phenolic resin changes from the liquid to a gel state. It is an indication of the cure rate of a phenolic resin under certain conditions.

Phenolic resins suitable for the manufacture of abrasives may optionally contain plasticizers, cross-linking aids or other modifiers. Modifiers are used to overcome the deficiencies of phenolic resins in certain applications, such as brittleness in the cured state and lack of water tolerance in the uncured state. Modifiers were previously used to adjust the physical properties of the final product, e.g. hardness in a humid environment, but many required additional VOCs to reduce viscosity.

Nitroalkanes and urea are known to react with formaldehyde, but these compounds have not, to the knowledge of the inventors, been used as reactive diluents in the manufacture of abrasives. Poly(oxyalkylene)amines are also known to react with phenolic resins and there have been attempts by the assignees to commercialize nonwoven abrasives containing poly(oxyalkylene)amines with a molecular weight of 400 and above. These attempts have been essentially unsuccessful. The high molecular weight poly(oxyalkylene)amines typically require an organic solvent to make the binder prepolymer solution in which they are mixed coatable.

U.S. Patent No. 4,571,413 to Dolden et al. describes the use of polyethers [poly(oxyalkylene)diamines] in the preparation of modified phenolic resins for use in fiber reinforced composites and phenolic foams. Improved impact strengths and improved flexural properties are specifically mentioned. 2-45 parts polyester per 100 parts aqueous phenolic resin are suggested. All resole resins are acid catalyzed. No mention is made of base catalysis, applicability to abrasive compositions, or VOC reduction.

U.S. Patent No. 4,786,683 to Schloman, Jr. et al. describes guaiacol resins containing poly(oxyalkylene)amines and phenolic resins for use as rubber modifiers.

U.S. Patent No. 4,163,030 to Banucci et al. describes blends of polyether amide-imide compounds and phenolic resins. The applicability for solventless, dry powder coatings and electrical insulation is specifically mentioned.

U.S. Patent No. 3,734,965 to Becker describes poly(oxyalkylene) compounds with aldehydes and substituted phenols as curing agents for epoxy resins.

U.S. Patent No. 4,226,971 to Waddill et al. describes an epoxy curing agent obtained from the phenol-aldehyde condensation product and the aminoalkylene derivative of a poly(oxyalkylene)polyamine.

U.S. Patent No. 3,933,936 to Smith et al. describes aziridine-modified phenolic resins with good bonding to wood, metal, ceramics and plastics and that cure quickly. There is no mention of abrasive applications, poly(oxyalkylene) compounds or VOC reduction.

U.S. Patent No. 4,650,838 to Das et al. describes aromatic phthalocyanine compounds as modifiers for phenolic resins. Special mention is made of improved thermal stability and applicability in abrasives. Novolaks or resol-based novolaks are the focus.

U.S. Patent No. 5,041,481 to Sugimori et al. describes amino compounds as adhesion promoters for curable compositions such as paints, adhesives or sealant compounds.

U.S. Patent No. 4,102,866 to Speranza et al. describes poly(oxyalkylene) compounds as curing agents for epoxy novolac resins.

U.S. Patent No. 4,164,420 to Waddill et al. describes a process that uses poly(oxyalkylene) compounds to accelerate the curing of epoxy resins.

British Patent No. 1,501,331 of the Minnesota Mining and Manufacturing Company describes the use of poly(oxyalkylene) compounds with epoxy resins to make abrasives.

U.S. Patent No. 4,906,774 to Speranza et al describes the preparation of a urea-bound diamine product from poly(oxyalkylene)diamines and diisocyanates.

U.S. Patent No. 4,154,724 to Schulze describes the preparation of poly(oxyalkylene) compounds with ureido functional groups.

U.S. Patent No. 5,039,759 (Hoy et al.) discloses the use of reactive urea, thiourea and carbamate derivatives as extenders and reactive diluents for modifying water-dispersible resins, including polyester alkyd resins, carboxylated hydroxy group-containing epoxy fatty acid esters, carboxylated polyesters, carboxylated alkyd resins, carboxylated acrylic copolymers without amide groups and carboxylated vinyl copolymers. Although usefulness in these systems is disclosed, there is no indication of the use of reactive urea, thiourea or carbamate derivatives as reactive diluents in phenolic or urea-aldehyde resin systems.

US Patent No. 3,862,060 (Anderson) describes stable emulsions containing thermosetting phenol-formaldehyde resole resins in high concentrations as the disperse phase. The emulsions have a water tolerance of less than 40 percent and are stabilized with a protein-containing compound. The resole resins are treated with amine catalysts and they are preferably modified with melamine. The emulsions optionally contain urea or dicyandiamide, which reduces free formaldehyde.

U.S. Patent No. 5,008,336 (Richey Jr. et al.) describes trisubstituted amino oxides having at least two reactive hydroxy groups that are useful as reactive diluents in polyol polymer-containing coating compositions.

U.S. Patent No. 4,903,440 (Larson et al.) describes a modified phenolic resole resin for use in abrasives containing a binder having at least 1.1 α,β-unsaturated carbonyl group side chains per molecule, but it does not indicate any advantages in the storage stability of the compositions described therein or the compositions themselves.

U.S. Patent No. 3,817,976 (Bakul et al.) discloses the use of a butadiene nitrile rubber as a modifier, but the use of additional organic solvents is necessary.

U.S. Patent No. 4,505,712 (Floyd et al.) and U.S. Patent Nos. 4,345,063; 4,285,690; 4,332,586; and 4,284,758 (North) describe the use of cyclic urea derivatives for treating textile fabrics and paper in the absence of formaldehyde, but additions of organic solvents are also required.

U.S. Patent No. 4,927,431 (Buchanan et al.) describes a modified phenolic resin binder for use in abrasives that contains an irradiation-curable component containing acrylate side chains, but requires the addition of organic solvents.

U.S. Patent No. 5,026,405 (Guerro) describes a modified phenolic resin in which certain alkyl or hydroxyalkylcarbamylmethyltriazines are mixed, whereby the moisture resistance of bonded abrasives is improved. However, the dry resistance of the abrasives is reduced.

U.S. Patent No. 4,802,896 (Law et al.) discloses a modified phenolic resin binder for use in abrasives containing a thermally stable aromatic ligand. This composition also requires the addition of organic solvents.

U.S. Patent No. 4,904,516 (Creamer) describes a water-soluble phenolic resin containing a soluble alkaline earth metal salt for use in binding fiberglass batting.

Other patents of interest include U.S. Patent Nos. 4,802,896; 4,904,516; 4,785,073; 4,311,631; 4,515,835; 4,108,840; 4,786,683; 4,163,030; 3,734,965; 3,933,936; 4,650,838; 5,041,481; 4,102,866; 4,164,520; British Patent Nos. 1,501,331; 4,906,774; 4,154,724; 3,862,060; 5,008,336; 4,903,440; 3,817,976; 4,505,712; 4,345,063; 4,285,690; 4,332,586; 4,284,758; 4,927,431 and 5,026,405.

As VOC emissions are increasingly regulated, there is an unmet need in the field of abrasives manufacturing for coatable, thermally curable binder prepolymer solutions that reduce or substantially eliminate the use of VOCs.

The present invention overcomes or reduces many of the above-mentioned problems associated with previously known coatable, thermally curable binder prepolymer solutions. In accordance with the present invention, coatable, thermally curable binder prepolymer solutions are provided with excellent water tolerance, gel time comparable to or less than previously known binder prepolymer solutions, and reduced VOC emissions. The binder prepolymer solutions enable the abrasives to exhibit a cutting performance after curing that is equal to that of abrasives made with previously known binder prepolymer solutions. In addition, the diversity of the individual embodiments of the reactive diluents allows the abrasives of the invention to be placed between the epoxy-based and phenolic-based binders in flexibility and hardness.

Coatable, thermally curable binder prepolymer solutions in accordance with the invention are characterized by comprising a 30-95% solids solution, more preferably a 60-80% solids solution, of a thermally curable resin having a plurality of pendant methylol groups and the balance of the solution being water and a reactive diluent.

The term "coatable" as used herein means that the solutions of the invention can be readily coated or sprayed onto substrates using coating equipment conventional in the abrasive arts such as knife coaters, roll coaters, continuous line coaters, electrospray coaters and the like. This property can also be expressed in terms of the viscosity of the solutions. The viscosity of the coatable, thermally curable binder prepolymer solutions should not exceed 2000 centipoise as measured using a Brookfield viscometer, spindle number 2, 60 rpm at 25°C. The term "percent solids" means the amount of organic material in weight percent that remains when the curing conditions are applied. Because of VOC emissions, it is not practical to use a solids content below 30%, while at solids levels above 95%, the resin solutions are difficult to coat even when heated. The term "thinner" is used in the sense that the reactive diluent the concentration of the thermally curable resin in the solutions of the invention is diluted and does not mean that the viscosity of the solutions necessarily decreases.

The thermally curable resin is the reaction product of a compound that is not an aldehyde and an aldehyde, wherein the compound that is not an aldehyde is selected from the group consisting of ureas and phenolic substances.

The reactive diluent has at least one functional group that is independently reactive with the pendant methylol groups and with the aldehyde and that is selected from the group consisting of

A) Compounds selected from the group consisting of compounds of the general formula

and mixtures thereof, wherein X = O or S and Y = -NR³R⁴ or -OR⁵, with the proviso that if X = S, Y = NR³R⁴, each of R¹, R², R³, R⁴ and R⁵ is a monovalent radical selected from the group consisting of a hydrogen atom, alkyl radicals having 1 to 10 carbon atoms, hydroxyalkyl radicals having 2 to 4 carbon atoms and one or more hydroxy groups, and hydroxypolyalkyleneoxy radicals having one or more hydroxy groups, and with the provisos that:

(i) the compounds contain at least one -NH and one OH group or at least two -OH groups or at least two -NH groups;

(ii) R¹ and R² or R¹ and R³ may be bonded together to form a ring; and

(iii) R¹, R², R³, R⁴ and R⁵ cannot each simultaneously represent a hydrogen atom;

B) compounds having a molecular weight of less than 300 selected from the group consisting of alkyl-substituted 2-amino alcohols, β-ketoalkylamides and nitroalkanes;

C) poly(oxyalkylene)amines having a molecular weight in the range of 90 to 300; and

D) Poly(oxyalkylene)ureido compounds having a molecular weight in the range of 90 to 1000.

Preferred reactive diluents further include the compounds characterized in that X is O, Y = NR3R4, R1 is a 2-hydroxyethyl group, R2 and R3 are bonded together to form an ethylene bridge, and R4 is a hydrogen atom.

A preferred alkyl-substituted 2-amino alcohol useful as a reactive diluent is 2-amino-2-methyl-1-propanol, while a preferred β-ketoalkylamide is β-ketobutyramide.

In addition, nitroalkanes having at least one active hydrogen atom bonded to the α-carbon atom purify coatable, thermally curable binder prepolymer solutions of the present invention from formaldehyde.

Typical poly(oxyalkylene)amines include poly(oxyethylene-co-oxypropylene)amine, poly(oxypropylene)amine and poly(oxypropylene)diamine, while typical poly(oxyalkylene)ureido compounds are the reaction product of urea and the previously identified poly(oxyalkylene)amines.

Optionally, the coatable, thermally curable binder prepolymer solutions of the invention may include up to 50 weight percent (of the total weight of the thermally curable resin) of ethylenically unsaturated monomers. The monomers, e.g., tri- and tetraethylene glycol diacrylate, are curable by radiation and may reduce the overall cure time of the thermally curable resins by providing a mechanism for pre-cure gelation of the thermally curable resin.

Another embodiment of the invention is an abrasive characterized by a plurality of abrasive grains dispersed and adhered in a binder, the binder consisting of a coatable, thermally curable binder prepolymer solution having substantially reduced emissions of VOC, the binder prepolymer solution comprising the reaction product of a 30-95% solids solution of a thermally curable resin having a plurality of pendant methylol groups, the balance comprising water and a reactive diluent, preferred resins and reactive diluents being those described above, and when the reactive diluent is a poly(oxyalkylene)amine, the molecular weight is in the range of 90 to 1000, provided that if the abrasive is a nonwoven abrasive, the molecular weight of the poly(oxyalkylene)amine is less than 300.

Particularly preferred are coated, nonwoven and bonded abrasives, which contain the preferred binders.

Abrasives manufactured using the materials and processes described here exhibit excellent resistance to degradation, particularly in wet environments, and give the abrasive manufacturer a high degree of flexibility in producing abrasives with different degrees of flexibility. An advantage of the processes for making abrasives in accordance with the teachings herein is reduced emissions of VOCs.

Figures 1 and 2 show enlarged cross-sectional views of coated abrasives made in accordance with the present invention;

Fig. 3 is an enlarged schematic view at approximately 100x magnification of a nonwoven abrasive article in accordance with the invention;

Figure 4 graphically shows that as the amount of reactive diluent hydroxyethylethyleneurea (HEEU) in the binder prepolymer solutions of the present invention increased, the total formaldehyde emission decreased to 55% of the emitted formaldehyde from an unmodified sample;

Figure 5 graphically shows that increased amounts of the alkaline catalyst in the binder prepolymer solutions of the present invention tended to increase the rate of formaldehyde emission, but the cumulative formaldehyde emission was reduced to 66% of the formaldehyde emitted from an unmodified sample of the binder prepolymer solution containing the phenol-formaldehyde resin;

Figures 6 and 7 show graphically that combinations of the alkaline catalyst and the reactive diluent HEEU in binder prepolymer solutions of the present invention that included phenol-formaldehyde resins reduced formaldehyde emissions to 56% and 46% of the formaldehyde emitted from an unmodified (i.e., without reactive diluent) sample of the same prepolymer solution; and

Figures 8 and 9 show, graphically, that the reactive diluents 2-amino- 2-methyl-1-propanol (Fig. 8) and α-ketobutyramide (Fig. 9) reduced formaldehyde emissions from coatable, thermally curable binder prepolymer solutions containing phenol-formaldehyde resins.

Fig. 10 shows graphically that the reactive diluent nitromethane reduced the formaldehyde emissions.

The term "coatable, thermally curable binder prepolymer solution" as used herein means a coatable, homogeneous mixture including the uncured thermally curable resin, the reactive diluent and water which forms a binder upon curing. The term "binder" means a cured binder. The term "thermally curable resins" as used herein means phenol-aldehyde or urea-aldehyde resins which may include up to 50% by weight of one or more ethylenically unsaturated monomers such as triethylene glycol diacrylate which are sometimes used to gel or precure the thermally curable resins by providing a monomer which can be cured by irradiation (and thus reduce the time necessary for thermal curing). The thermally curable resins are thus the reaction product of a compound, which is not an aldehyde and an aldehyde which, upon curing, may exhibit an interlocking radiation-curable polymeric network. A compound which is not an aldehyde includes urea, straight-chain and branched alkyl-substituted ureas and aryl-substituted ureas as well as phenol, alkyl- and aryl-substituted phenols including cresols, xylenols, resorcinol, p-tert-butylphenol, p-phenylphenol and nonylphenol and diphenols, e.g. bisphenol-A. The "methylol group" means a radical having a terminal -CH₂OH group.

In accordance with the present invention, the term "reactive diluent" refers to a class of compounds having at least one functional group that is independently reactive with the pendant methylol groups of the thermally curable resin and with aldehydes, and that has the ability to "scavenge" the unreacted aldehydes when the coatable, thermally curable binder prepolymer solution cures. Preferably, reactive diluents used in the coatable, thermally curable binder prepolymer solutions of the present invention are low or medium molecular weight compounds, typically having a molecular weight in the range of 60 to 1000. Reactive diluents having molecular weights of less than 600 are preferred, particularly preferred are those having a molecular weight of less than 300. Reactive diluents useful in the invention have solubility parameters that enable the coatable, thermally curable binder prepolymer solution to avoid phase separation during processing (or increase water tolerance) when diluted with water.

Typical functional groups reactive with either methylol groups of the thermosetting resin or with aldehydes and useful in the present invention are R'-NH-R"; -NR'R"; and -NR'(C=O)-NR"R"', where R', R" and R"' may represent a hydrogen atom or substituted or unsubstituted hydrocarbon radicals, but when substituted, the substituent or substituents should not inhibit or prevent the reaction with the methylol groups or aldehydes. Typical examples of the substituents for R include an alkyl radical, e.g., methyl, ethyl, an aryl radical, e.g., phenyl, an alkoxy radical and a carbonyl group. Typical and preferred other functional groups reactive with methylol groups are -OH, -NH₂; and H₂N-C-O)-NH-. If the reactive diluent has an aldehyde group as a functional group, it will be substituted on the aromatic phenol ring.

A chemical group of particularly preferred reactive diluents which fulfil the above preferred features includes the compounds represented by the general formula:

and mixtures thereof, wherein X = O or S and Y = -NR³R⁴ or -OR⁵, with the proviso that if X = S, Y = NR³R⁴, R¹, R², R³, R⁴ and R⁵ each represent a monovalent radical selected from the group consisting of a hydrogen atom, alkyl radicals having 1 to 10 carbon atoms, hydroxyalkyl radicals having 2 to 4 carbon atoms and one or more hydroxy groups, and hydroxypolyalkyleneoxy radicals having one or more hydroxy groups, and with the provisos that:

(i) the compound contains at least one -NH and one -OH group or at least two -OH groups or at least two -NH groups;

(ii) R¹ and R² or R¹ and R³ may be bonded together to form a ring structure; and

(iii) R¹, R², R³, R⁴ and R⁵ cannot each simultaneously be a hydrogen atom.

Typical examples of reactive diluents useful in the practice of the invention and represented by the general formula (I) include the compounds wherein X is O, Y = NR³R⁴, R¹ is 2-hydroxyethyl group, R² and R³ are bonded to each other to form an ethylene bridge, and R⁴ is hydrogen atom or hydroxyethyl ethylene urea, known under the trade name "UCAR RD-65-2" from Union Carbide Corporation, and the compounds wherein X is O, Y = NR³R⁴, R¹ and R³ are hydrogen atom, R² is butyl group, and R⁴ is a hydroxyethyl-(N-2-hydroxyethyl-N'-butylurea), N,N'-bis-(2-hydroxyethyl)-N'-butylurea or N,N'-bis-(2-hydroxyethyl)urea group.

Other urea compounds useful as reactive diluents in the present invention are listed in column 7 of U.S. Patent No. 5,039,759.

Typical examples of reactive diluents useful in the practice of the present invention are thiourea compounds represented by the above general formula (I) wherein X is only S. Similarly, examples of typical reactive diluents representing carbamates in the above general formula (1) include 2-hydroxyethyl-1-butylcarbamate, 1,2-hydroxyethyl-1-butylcarbamate, 1,2-hydroxyethylcarbamate and other carbamates listed in column 9 of U.S. Patent No. 5,039,759.

The preparation of the above-mentioned ureas, thioureas and carbamates is carried out by methods known in the art. The preparation of N-(2-hydroxyethyl)-N,N'-ethyleneurea can, for example, be carried out by reacting equimolar mixtures of aminoethylethanolamine and dimethylcarbamate in a nitrogen-purged vessel by heating (80°C). The mixture is stirred for three hours and then allowed to stand overnight. The mixture is then reheated to 195ºC, recovering methanol and other volatiles. The material remaining in the vessel is then subjected to vacuum distillation to obtain a distillate of the urea. Details of the preparation of this and other ureas are disclosed in U.S. Patent No. 5,039,759, columns 9-13.

Another chemical group of particularly preferred reactive diluents are the poly(oxyalkylene) compounds, such as poly(oxyalkylene)amines (POAA) and poly(oxyalkylene)ureides having a molecular weight in the range of 90 to 1000. The poly(oxyalkylene) compounds useful in the invention may, but need not, have a functional amino group.

One group of useful poly(oxyalkylene)amines are monoamines selected from the group consisting of compounds of the general formula

where R6 is an alkyl radical having 1 to 4 carbon atoms and n and m are integers in the range of 0 to 20.

Useful poly(oxyalkylene)amines, which are diamines, are selected from the group consisting of compounds of the general formula

where x is an integer in the range from 2 to 20. A variation of this are the poly(oxyalkylene)amines selected from the group consisting of compounds of the general formula

where a, b and c are integers, the sum of a plus c is from 1 to 5 and b is from 0 to 20. Finally, poly(oxyalkylene)amines which are triamines and are useful in the invention are selected from the group consisting of compounds of the general formula

where m, n and o are integers greater than 0, with the proviso that the sum of m, n and o is from 5 to 30, and where A is a triol initiator, e.g. trimethylolpropane, glycerin and the like.

Typical examples of poly(oxyethylene)amine based reactive diluents useful in the practice of the invention include: poly(oxyethylene-co-oxypropylene)amine, poly(oxypropylene)amine, poly(oxypropylene)diamine, poly(oxyethylene-co-oxypropylene)diamine, poly(oxyethylene-co-oxypropylene)urea, poly(oxyethylene-co-oxypropylene)diurea, and trifunctional reaction products of glycerin or trimethylolpropane with hydroxy terminated poly(oxypropylene)amine. Poly(oxyethylene)amine based reactive diluents are available under the trade designation "Jeffamine" from Texaco Chemical Company, Houston, Texas.

As mentioned above, the reactive diluents in accordance with the invention have two reactive functional groups: one reactive functional group of the reactive diluent reacts either with the methylol groups of a thermally curable resin A to produce our intermediate B, or with the aldehyde to produce an intermediate C. The intermediate C then reacts with the compound A to produce a second intermediate D. The other reactive functional group of the reactive diluent, in this case on intermediate B, then reacts with a methylol group of intermediate D to produce an intermediate E, and so on. In this way, the reactive diluents useful in the present invention have the ability to "scavenge" (i.e., convert and bind them into the cured mass) aldehydes that would otherwise be emitted to the workplace and the open environment.

Reactive diluents useful in the binder prepolymer solutions of the present invention preferably have a solubility parameter of at least 12 (cal-cm⁻³)1/2 (commonly known as Hildebrand units). Solubility parameters above this value result in the preparation of coatable, thermally curable binder prepolymer solutions with higher water tolerance. A discussion of the Solubility parameters of organic compounds and their derivation from physical data are given in The Handbook of Chemistry and Physics, 58th edition, pages C-726-C-732, published in 1977 by CRC Press, Inc., West Palm Beach, Florida.

For a coatable, thermally curable binder prepolymer solution in accordance with the present invention containing 100 parts of a standard phenolic resin to 10 parts of the HEEU reactive diluent, the water tolerance is in the range of 70 to 260 percent by weight of water based on the weight of the phenolic resin. The high water tolerances are achieved by increasing the amount of alkaline catalyst. The lower water tolerance of 70 percent by weight is typically achieved with a reactive diluent alone and no additional alkaline catalyst, while the higher water tolerance is achieved with an additional 3.2 parts of the alkaline catalyst and 10 parts of the reactive diluent based on a standard phenolic resin containing 2% potassium hydroxide per weight of the phenol. In a coatable, thermally curable binder prepolymer solution of the invention with 100 parts of the standard phenolic resin and 15 parts of the reactive diluent HEEU, with the same amount of alkaline catalyst, the water tolerance is in the range of 90 to 320 percent by weight.

Other structural classes of reactive diluents useful in the invention having similar properties to the aforementioned ureas, thioureas and carbamates (i.e., having at least one functional group reactive with the methylol groups of the thermally curable resin and having at least one functional group reactive with aldehydes) can be used in the coatable, thermally curable binder prepolymer of the present invention. One class includes alkyl-substituted 2-amino alcohols such as 2-amino-2-hydroxymethyl-1,3-propanediol, 2-aminoethanol, 2-amino-2-methyl-1-propanol, 2-amino-1-butanol, 2-amino-2-methyl-1,3-propanediol, 2-amino-2-ethyl-1,3-propanediol and 2-amino-2-hydroxymethyl-1,3-propanediol. These components react with aldehydes, for example formaldehyde, according to the following reaction:

Another class of reactive diluents useful in separating the coatable, thermally curable binder prepolymers of the present invention from formaldehyde includes β-ketoalkylamides such as β-ketobutyramide (IX) available from Eastman Chemicals, which has the following structure:

Aldehydes are known to react with compounds containing "active methylene group" compounds such as (IX) to produce a number of stable condensation products. N-substituted β-ketobutyramides obtained from the reaction of diketene with amino alcohols such as 2-aminoethanol, 2-amino-2-methyl-1-propanol, 2-amino-1-butanol, 2-amino-2-methyl-1,3-propanediol, 2-amino-2-ethyl-1,3-propanediol and 2-amino-2-hydroxymethyl-1,3-propanediol can also act as reactive diluents in phenolic resins to provide better compositions that purify from aldehyde, provide improved water tolerance and provide better properties of the final resin product.

As mentioned above, nitroalkanes, e.g., nitromethane, nitroethane, 2-nitropropane, having at least one active hydrogen atom bonded to the α-carbon atom, also scavenge formaldehyde in a coatable, thermally curable binder prepolymer solution of the present invention.

The thermally curable resins employed in the coatable, thermally curable binder prepolymer solutions of the present invention are preferably selected from the group consisting of phenolic and urea-aldehyde resins and mixtures thereof. The resins comprise the reaction product of an aldehyde and a non-aldehyde compound. Phenolic resins are preferred because of their thermal properties, availability, low cost and ease of handling. The general term "phenolic" includes both phenol-formaldehyde resins and resins comprising other phenol derivatives and aldehydes. The thermally curable resins are preferably 30-95% solids, more preferably 60- 80% solids, having a viscosity in the range of 750 to 1500 cps (Brookfield viscometer, spindle number 2, 60 rpm, 25ºC) before the addition of water and the reactive diluent, and having a molecular weight (number average) of at least 200, preferably in the range of 200 to 700.

Suitable alkaline catalysts for catalyzing the reaction between the aldehyde and phenolic components of the phenolic resole resins include sodium hydroxide, barium hydroxide, potassium hydroxide, calcium hydroxide, organic amines and sodium carbonate, all as solutions of the catalyst dissolved in water. Typical commercially available phenolic resins contain the alkaline catalyst in an amount of 2% by weight based on the weight of the phenolic component. Typically the additional catalyst solution comprising a 50% (weight of total) solution of sodium hydroxide (NaOH) may be added to adjust the water tolerance and assist in further increasing the molecular weight.

Cured phenolic resole resins are particularly preferred as binders for abrasive grains. However, when uncured phenolic resins are processed with water, as is common to reduce VOC emissions, the uncured phenolic binder prepolymer solution undergoes partial phase separation due to its molecular weight and only partial water solubility. The present invention essentially overcomes the problem by mixing the uncured phenolic resole resin with a reactive diluent having the properties and structure described herein. The coatable, thermally curable binder prepolymer solutions of the present invention have improved water tolerance, substantially equal gel times and very low levels of VOC compared to unmodified 100% (weight of total resin) phenolic resins. The coatable, thermally curable binder prepolymer solutions of the present invention utilizing reactive diluents represented by general formula I produce abrasives having a grinding performance substantially equal to that of unmodified 100% (weight of total resin) phenolic resin-based abrasives. The coatable, thermally curable binder prepolymer solutions of the present invention utilizing poly(oxyalkylene)amine-based reactive diluents produce abrasives having a hardness and flexibility intermediate between that of unmodified 100% (weight of total resin) phenolic resin-based abrasives and 100% epoxy resin-based abrasives.

Aldehydes useful in producing the thermally curable resins useful in the coatable, thermally curable binder prepolymer solutions of the present invention include cyclic, straight chain and branched alkyl aldehydes, which may be saturated or unsaturated, and aromatic aldehydes. The aldehydes preferably have a molecular weight below 300, thereby yielding a less viscous binder prepolymer solution. Examples of suitable aldehydes include formaldehyde, benzaldehyde, propanal, hexanal, cyclohexanecarboxaldehyde, acetaldehyde, butyraldehyde, valeraldehyde and other low molecular weight aldehydes. Formaldehyde is preferred because of its availability, low cost, cured resin properties and because it provides low viscosity binder prepolymer solutions.

Both phenolic resole and novolak resins (including resoled novolaks) are heat cured. Phenolic novolak resins require a formaldehyde source, e.g. hexamethylenetetramine or a resole, to effect cure. Temperature and pH significantly affect the polymerization mechanism and the final properties of the cured resin. Examples of commercially available phenolic resins include those sold under the trademarks "Varcum" (from BTL Specialty Resins Corp.), "Aerofene" (from Ashland Chemical Co.), and "Bakelite" (from Union Carbide). A standard, 70% solids, 1.96:1.0 phenolic formaldehyde/phenol resin containing 2 wt.% KOH based on the weight of the phenol is available from Reichold Chemicals, Mississauga, Ontario, Canada.

Although the reactive diluent is preferably premixed with the thermally curable resin to prepare the coatable, thermally curable binder prepolymer solutions of the invention, for some reactive diluents, such as the POAA diluents, the thermally curable resin may be premixed with an amount of water sufficient to absorb some of the exothermic heat given off when the POAA is mixed with the resin. The weight ratio of resin to the reactive diluent may range from 2:1 to 100:1 for all reactive diluents useful in the invention, and from 1:1 to 100:1 for the POAA reactive diluents. Typically, a necessary amount of a suitable solvent is then added to render the binder prepolymer solution coatable. The solvent is preferably water for all reactive diluents useful in the invention, but those skilled in the art will recognize with little experimentation that an organic solvent may be necessary depending on the coating process chosen. When water is used as a solvent, it is preferably added to the water tolerance level of the binder prepolymer solution, although this is not necessary. A water tolerance greater than 100% is preferred, greater than 150% is particularly preferred.

Ethylenically unsaturated monomers may also be added to the coatable, thermally curable binder prepolymer solutions of the invention, provided that if the ethylenically unsaturated monomer selected is an acrylate, the reactive diluent must not have a terminal amino group. Ethylenically unsaturated monomers are sometimes added to thermally curable resins to provide a gelling mechanism using a suitable radiation source to create an interlocking polymer network in the thermally curable resin.

Ethylenically unsaturated monomers suitable for the present invention include monomeric or polymeric compounds containing carbon, hydrogen and oxygen atoms, and optionally nitrogen and halogen atoms. Oxygen and nitrogen atoms are generally present in ether, ester, urethane, amide and urea moieties. The compounds preferably have a number average molecular weight of less than 4,000.

Preferred compounds are esters of aliphatic monohydroxy and polyhydroxy radical-containing compounds and unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid and the like. Typical examples of preferred ethylenically unsaturated compounds include methyl methacrylate, ethyl methacrylate, styrene, divinylbenzene, vinyltoluene, ethylene glycol diacrylate and methacrylate, hexanediol diacrylate, tri- and tetraethylene glycol diacrylate and methacrylate, trimethylolpropane triacrylate, glycerol triacrylate, pentaerythritol triacrylate and methacrylate, pentaerythritol tetraacrylate and methacrylate, dipentaerythritol pentaacrylate, sorbitol triacrylate, sorbitol hexaacrylate, bisphenol A diacrylate and ethoxylated bisphenol A diacrylate.

Other ethylenically unsaturated compounds useful in the invention include ethylene glycol diitaconate, 1,4-butanediol diitaconate, propylene glycol dicrotonate, dimethyl maleate, and the like. Other ethylenically unsaturated compounds include monoallyl, polyallyl, and polymethallyl esters and amides of carboxylic acids such as diallyl phthalate, diallyl adipate, and N,N-diallyladipamide. Still other nitrogen-containing compounds include tris(2-acryloyloxyethyl)isocyanurate, 1,3,5-tri(2-methacryloxyethyl)-s-triazine, acrylamide, ethacrylamide, N-methylacrylamide, N,N-dimethylacrylamide, N-vinylpyrrolidone, and vinylpiperidone. Acrylics are preferred as ethylenically unsaturated compounds because of their ready availability and increased cure rate.

The coatable, thermally curable binder prepolymer solutions of the present invention are cured primarily by heat, but to achieve partial gelation, radiant energy may be used, depending on whether ethylenically unsaturated compounds are added to accelerate curing.

When the binder prepolymer solution is cured by heat alone, the temperature of the curing environment should be set at a minimum of 100ºC and the binder prepolymer solution should be kept at this temperature for a minimum of 4 hours. Curing can be carried out in a shorter time at higher temperatures. In the case of coated and non-woven abrasives, the curing temperature is limited to the temperature that the synthetic and natural backings used in the abrasives can withstand.

If the binder prepolymer solution can be partially cured by irradiation, the amount of radiation used depends on the degree of cure desired and the individual monomers used to prepare the binder prepolymer solution.

Examples of radiant energy sources include ionizing radiation, ultraviolet radiation and visible light. Ionizing radiation, e.g. electron beams, preferably has an energy level of 0.1 to 10 mrad, more preferably 1 to 10 mrad. Ultraviolet radiation has a wavelength within the range of 200 to 700 nanometers, more preferably between 250 to 400 nanometers. Visible light is radiation having a wavelength in the range of 400 to 800 nanometers, more preferably between 400 to 550 nanometers. The rate of curing at a given level of radiation varies according to the thickness of the binder, the temperature, as well as the density and type of composition. Ultraviolet radiation obtained with a lamp power of 79 watts/cm is preferred. At this power, the binder prepolymer solutions should be exposed at a rate of 30 m/min.

Optionally, a thermal initiator may be added to increase the rate of thermal curing. Examples of thermal initiators include peroxides, e.g. benzoyl peroxide, and azo compounds.

When the coatable, thermally curable binder prepolymer solution is first partially cured by ultraviolet irradiation, a photoinitiator is necessary to initiate the free radical polymerization. Examples of the photoinitiators are organic peroxides, azo compounds, quinones, benzophenones, nitroso compounds, acyl halides, hydrazones, mercapto compounds, pyrylium compounds, triacrylimidazoles, bisimidazoles, chloroalkyltriazines, benzoin esters, benzil ketals, thioxanthones, and acetophenone derivatives. Further references to free radical photoinitiator systems for ethylenically unsaturated compounds are described in U.S. Patent Nos. 3,887,450; 3,895,949; and 3,775,113. Another good reference to photoinitiator systems for free radicals is given in J. Kosar, Light-Sensitive Systems, J. Wiley and Sons, Inc. (1965), especially Chapter 5.

If the coatable, thermally curable binder prepolymer solution can be cured by exposure to visible light, a photoinitiator is required to initiate free radical polymerization. Examples of preferred photoinitiators can be found in U.S. Patent No. 4,735,632.

The coatable, thermally curable binder prepolymer solutions of the present invention may contain fillers, fibers, lubricants, grinding aids, wetting agents, and minor amounts of other additives such as surfactants, pigments, dyes, coupling agents, plasticizers, and suspending agents. The amounts of these materials are selected to provide the desired properties.

Coated abrasives which can be prepared by cured forms of the coatable, thermally curable binder prepolymer solutions of the invention are illustrated in the enlarged cross-section in Figs. 1 and 2. As shown in Fig. 1, the coated abrasive, generally designated 10, includes a flexible backing 12, e.g., a sheet of paper or a web of cloth, optionally coated with an impregnating coating (not shown) which may optionally be treated with a size coat on the back surface 14 and/or optionally with a size coat on the front surface 16. Over the size coat on the front surface is layered a coating formation 18 in which abrasive grains 20, such as silicon carbide or aluminum oxide abrasive grains, are embedded. A size coat 22 has been placed over the coating formation 18 and the abrasive grains 20. There is typically no clear line of demarcation between the impregnating coating, the size coat on the back surface and the size coat on the front surface which meet inside the fabric backing which is saturated as much as possible with resins of these coatings. Typical impregnating coatings may include soft acrylic latexes, natural rubber and the thermally curable resins described above. Back and front adhesive coatings may also include the thermally curable resins described here.

Illustrated in Fig. 2 is a coated abrasive, generally designated 30, formed on a paper backing 32. The paper backing 32 is treated with a size coat on the bottom surface 34 and a size coat on the front surface 36. The size coat on the front surface 36 is overcoated with a coating formation 38 in which abrasive grains 40 are embedded. The abrasive grains 40 and the coating formation 38 are overcoated with a size coat 42 which assists in adhering the abrasive grains 40 to the backing during use and may also contain grinding aids.

Fig. 3 shows an enlarged schematic view, at about 100x magnification, of one embodiment of a typical nonwoven abrasive article with its three components. The fibrous mat 50 is the substrate to which the abrasive grains 52 are adhered by the resinous binder 54.

Fillers are often used in abrasives to reduce costs and improve spatial stability and other physical properties. Fillers may be selected from any filler that does not adversely affect the properties of the binder. Preferred fillers include calcium carbonate, calcium oxide, calcium metasilicate, aluminum sulfate, alumina trihydrate, cryolite, magnesium oxide, kaolin, quartz and glass. Fillers that act as grinding aids include cryolite, potassium fluoroborate, feldspar and sulfur. The fillers may be used in various amounts limited only by the proviso that the abrasive retains satisfactory mechanical properties (such as flexibility and toughness).

The backing for coated abrasives can be made, for example, from paper, cloth, vulcanized fiber, a polymer film or any other backing material known for use in a coated abrasive or treated variations thereof.

The abrasive grains may be of any type used to make coated abrasives and may be, for example, flint, garnet, alumina, ceramic alumina, alumina-zirconia (including fused alumina-zirconia as disclosed in U.S. Patent Nos. 3,781,172; 3,891,408; and 3,893,826 and commercially available from Norton Company of Worcester, Massachusetts under the trade designation "NorZon"), cutting diamond, silicon carbide (including refractory coated silicon carbide as disclosed in U.S. Patent No. 4,505,720), alpha-alumina based ceramic material (available from Minnesota Mining and Manufacturing Company under the trade designation "CUBITRON") as disclosed in U.S. Patent Nos. 4,314,827; 4,518,397; 4,574,003; 4,744,802; and EP Publication 228,856, or mixtures thereof. The abrasive grains can be used individually or as an agglomerate. The quantitative distribution of the abrasive grains on the backing is within the usual range. The abrasive grains can be oriented depending on the requirements of the individual coated abrasive or they can be applied to the backing without orientation.

Coated abrasives made in accordance with the present invention may also include modifications as are known in the art. For example, a backing coating, e.g., a pressure sensitive adhesive (PSA), may be applied to the non-abrasive side of the backing and various special size coats, such as zinc stearate, may be applied to the abrasive surface, thereby avoiding the abrasive stress; alternatively, the special size coat may contain a grinding aid to improve the abrasive properties of the coated abrasive, or a release coating, allowing easy separation of the PSA from the coated abrasive surface.

An advantage of the process for making the abrasives of the present invention over previously known processes is the reduction of VOC emissions from thread furnaces. The inclusion of amino or urea terminated reactive diluents in the coatable, thermally curable binder prepolymer solutions described herein significantly reduces formaldehyde emissions during curing of the binder prepolymer solutions and can also increase the water tolerance of the uncured binder prepolymer solution. Careful selection of the thermally curable resin and reactive diluent (use of a reactive diluent with a molecular weight of less than 1000) makes it possible to obtain coatable viscosities using water alone as the solvent. Organic solvents, which contribute to atmospheric VOCs are then not necessary to adjust the viscosity.

In making coated abrasives of the invention, the coatable, thermally curable binder prepolymer solutions of the present invention, when cured, can be used as a treatment coating for the backing, e.g., for cloth, paper, or a plastic layer, saturating or providing a coating on the backside (a back size coat) or a coating on the frontside (a front size coat) of the backing, as a coating to which the abrasive grains are first attached, as a size coat for adhering the abrasive grains to the backing, or for a combination of the coatings mentioned above. In addition, the coatable, thermally curable binder prepolymer solutions of the present invention, when cured, can be used in coated abrasives embodiments where only a single binder coating is applied, i.e., where a single coating takes the place of a coating/size coat composition.

When the coatable, thermally curable binder prepolymer solutions of the present invention are applied to a substrate in one or more treatment steps to form a treatment coating, the treatment coating can be thermally cured by passing the treated substrate over a heated drum; it is not necessary to festoon the substrate to fix the treatment coating or coatings. After the substrate has been well treated with a treatment coating, the coating can be applied. After the coating is applied, the abrasive grains are applied over the coating. The coating, now carrying the abrasive grains, is then exposed to a heat source, and optionally a radiation source, which generally sufficiently solidifies or fixes the binder, whereby the abrasive grains adhere to the substrate. It is preferred to use only the heat source to set the scale when no ethylenically unsaturated monomers are present. Thereafter, the size coat is applied and the size coat/abrasive grain/scale composition is exposed to a heat source, preferably via a drum hardener. The process will essentially harden or set the scale and size coat in the coated abrasive designs.

The coatable, thermally curable binder prepolymer solutions of the present invention need only be present, when cured, in at least one of the binder layers, ie, the treatment coat, the coating, the size coat, which comprises the coated abrasive. It need not be present in every make layer; the other make layers may use various other binders known in the art, e.g., epoxy-based binders. When the binder of the present invention is in more than one layer, the curing conditions for curing each layer of the coated abrasive need not be the same.

It is also contemplated that cured embodiments of the coatable, thermally curable binder prepolymer solutions of the present invention may be employed as a binder for nonwoven abrasives. Nonwoven abrasives typically include open, porous, raised fiber mats with abrasive grains bonded thereto by a binder. The process comprises, in a preferred embodiment, combining a 30-95% solids solution of a thermally curable resin with a reactive diluent as described above to form a coatable, thermally curable binder prepolymer solution, adding abrasive grains to the coatable, thermally curable binder prepolymer solution, coating the abrasive grain-filled, coatable, thermally curable binder prepolymer solution onto at least a portion of the fibers of a raised, open fibrous mat, and treating the resulting structure under conditions, preferably heat, sufficient to effect curing of the binder prepolymer solution. Optionally, additional abrasive grains may be applied prior to curing the binder prepolymer solution, for example, by electrostatic precipitation or by electrospraying. A suitable electrospray coating process is described in U.S. Patent No. 4,748,043 and is incorporated herein by reference.

Cured binder prepolymers of the present invention can also be used to make bonded abrasives. Bonded abrasives typically consist of a shaped mass of individual or agglomerated abrasive grains held together by an organic or ceramic binder material. The shaped, cured mass is preferably in the form of a grinding wheel. However, it is not necessary to mold the binder prepolymer solution and the abrasive grains prior to curing the binder prepolymer. The binder prepolymer and the abrasive grains can, for example, be poured onto a surface and cured into a flat bonded abrasive layer.

Investigation procedure

The following test methods were used to characterize the solutions and the products of the invention.

Water tolerance:

The amount of water (in percent of resin weight) that a phenolic resin tolerates before phase separation serves as an indicator of how much water is solvent can be added and how the molecular weight of the resin has increased. A 50.0 g sample of the resin to be tested was placed on a balance in a 250 ml beaker at 25ºC. While mixing the sample with a magnetic stirrer, small amounts of distilled water were added proportionately, the resin being mixed with the water after each addition of water until a homogeneous mixture was obtained. The end point was then reached when the resin/water solution began to take on a permanent milky appearance, that is, when the water and resin retain a milky appearance even after thorough stirring. After the end point was reached, the beaker and contents were weighed and the water tolerance is (AB) x 100% where A = final weight of beaker contents, B = weight of resin (initial weight).

Gelling time:

Gel time provides an indirect measure of the degree of polymerization for phenolic resins at a given amount of catalyst. The smaller the gel time, the greater the increase in the molecular weight of the resin is assumed to be. For each measurement, a commercially available gel time meter known under the trade name "Sunshine Gelmeter" available from Sunshine Co. was used. The gel time meter is a torsion device in which a glass rod (168 mm long, 6.35 mm diameter) is attached at one end via a chuck to a torsion wire (0.254 mm string wire, available from Sunshine Co.) and the torsion wire is then attached again via a magnetic clutch to a drive mechanism so that the wire/glass rod combination hangs vertically to the drive mechanism. 2.81 cm of wire was located between the chuck and the magnetic clutch. A test tube (150 x 18 mm) was filled to a depth of 65 mm with the resin being tested (equivalent to 25ºC ± 3ºC) and the tube placed in a boiling water bath. The glass rod was lowered into the tube so that the lower end of the glass rod was 6.35 mm from the bottom and the amount of resin in the tube was below the water bath level. The glass rod/torsion wire then rotated in the bath driven by the drive mechanism. As the combination rotated, a projection extending from the chuck connecting the glass rod and the torsion wire also rotated and eventually contacted a similar stationary projection extending from the machine. The distance between the projections was initially set at 2.38 mm for each test. The time taken for the rotating protruding part to contact the stationary protruding part was recorded as the gel time for each resin.

Micro Vickers hardness:

For all hardness measurements, a hardness tester known under the trade name "Leitz-Micro-Hardness" was used. The test procedure is described in ASTM E-92-82 (reaffirmed in 1987), which is hereby reference. In each case, a load of 50 grams was applied for 30 seconds to achieve the required indentation.

Machine direction (MD) and cross direction (CD) stretch tests:

All tests were conducted in accordance with ASTM D 1682, Method 2C-T, which is incorporated herein by reference.

Slate test in moist medium:

The test provided a measure of the cut (the material removed from the workpiece) and polish (the relative quality of the abraded surface) of coated abrasives under wet conditions. A 4-inch diameter circular coupon was ground from the abrasive material being tested and secured by a pressure-sensitive adhesive to a backing pad that had been preconditioned by soaking in water. The abrasive material was then placed in the water to pre-wet it. The backing pad was secured to the driven disk of a slate grinding tester (available from Frazier Precision Company, Gaithersburg, Maryland) that was placed vertically for testing in the wet medium. A 4-inch diameter, 1/2-inch thick circular acrylic plastic workpiece was used, available under the trade designation "POLYCAST" acrylic plastic from Seelye Plastics, Bloomington, Minnesota. The initial weight of each workpiece was recorded to milligrain accuracy prior to mounting the abrasive tester on the workpiece holder. The water drop velocity was set at 60 (+/- 6 grams) per minute. A 10-pound load was placed on the weight ramp of the abrasive tester and the mounted abrasive specimen was lowered onto the workpiece. The machine was set to run 500 cycles followed by an automatic stop. After each 500 cycles of the test, the workpiece was wiped clean of water and debris and then weighed. The cumulative cut of each test over 500 cycles was the difference between the initial weight and the weight after each trial.

To determine the polish of the workpiece, the ground workpiece was mounted in the specimen holder of a "Rank Surtronic 3" profilometer available from Rank Taylor-Hobson, Leicester, England, and the surface profile measured. For each test, Rtm, the mean of the maximum values of peak and depression of 5 specimen lengths, was recorded.

materials

The following materials were used as described in the examples (the quotation marks indicate trade names):

The chemical substance known under the trade name "EPON 871" is an epoxy resin available from Shell Chemical Company, Houston, Texas;

The chemical substance known under the trade name "EPON 828" is an epoxy resin available from Shell Chemical Company, Houston, Texas;

The chemical substance known under the trade name "VERSAMIDE 125" is a polyamide curing agent available from Henkel Corporation, Kankakee, Illinois;

The chemical substance known under the trade name "MODAFLOW" is a resin thinner available from Monsanto Company, St. Louis, Missouri;

The chemical substance known under the trade designation "A-1100" is a silane coupling agent available from Union Carbide Chemicals and Plastics Company, Inc., Danbury, Connecticut;

The chemical substance known under the trade name "AROMATIC 100" is a naphtha solvent available from Worum Chemical Company, St. Paul, Minnesota;

The chemical substance known under the trade name "SILWET L-7604" is a surfactant available from Union Carbide Chemicals and Plastics Company, Inc., Danbury, Connecticut; the chemical substance known under the trade name "INFERWET" is a nonionic surfactant available from Interstab Chemicals, New Brunswick, New Jersey;

The chemical substances known under the trade names "EDR-148", "D-230" and "ED-600" are poly(oxyalkylene)diamines available under the general trade name "JEFFAMINE" from Texaco Chemical Company, Houston, Texas, where the numerical designation indicates the approximate molecular weight of the compounds;

Grade 1200 silicon carbide abrasive grains are available from Nanko Abrasive Industry Company, Ltd., Tokyo, Japan;

Aluminium oxide abrasive grains of grade P-400 are available under the trade name "ALODUR FRPL" from Treibacher, Treibach, Austria;

DGMA is a diethylene glycol maleic anhydride polyester plasticizer;

"A" weight paper is a 110 gsm paper with a latex barrier coating that allows external application of a coating resin;

The chemical substance known under the trade name "Irgacure 651", a free radical initiator, is available from Ciba-Geigy Corp., Greensboro, North Carolina and

"PETA" is a pentaerythritol triacrylate monomer available from Sartomer Co. Inc., Exton, Pennsylvania.

"Hi-Sol 10" is a naphtha-based solvent available from Ashland Oil, Inc., Columbus, OH.

"Versacure 125 5C85" is a curing agent available from Henkel Corporation, Minneapolis, MN.

Examples

The following non-limiting examples will further illustrate the present invention. All coating weights are in grams/square meter (gsm). All parts and percentages of the resin formulation are based on weight, and the weight ratio of formaldehyde to phenol in the phenolic resin used to prepare the coatable, thermally curable binder prepolymer was 1.96:1 (standard phenolic resin with 2% KOH as catalyst, based on the weight of the phenol, available from Reichold Chemical) unless otherwise specified. The standard resin was also 70% solids unless otherwise specified, while the HEEU reactive diluent was 75% solids.

Comparative examples A-C and examples 1-6

In Comparative Examples A-C and Examples 1-6, the effects of the addition of the alkaline catalyst and various percentages of reactive diluents were demonstrated. While alkaline catalysts are known to increase the water tolerance of phenolic resins, the catalysts also result in greater water sensitivity of the cured binder and they result in binders that undergo greater physical changes with changes in processing conditions, such as ambient humidity.

Comparison examples A-C

Three standard phenolic phenol-formaldehyde resins (as mentioned above) were prepared with various amounts of additional alkaline catalyst (50% NaOH solution in water). Examples A, B and C had 0, 1.6 and 3.2 additional parts of 50% NaOH, respectively, and contained no reactive diluent. The three resins were cured at 110ºC for 18 hours. The water tolerance and gel time of the uncured resins and the Micro Vickers hardness values (dry and wet) of the cured resins were determined as shown in Tables 1, 2 and 3.

Examples 1-6

Six standard phenolic phenol-formaldehyde resins were prepared as in Examples AC, except that the reactive diluent HEEU was added in various amounts. Examples 1-6 were also cured at 110ºC for 18 hours. The water was a much higher water tolerance than the standard resin; and an increased addition of the alkaline catalyst resulted in comparable gel times and hardness values. Table 1. Water tolerance % Catalyst (as 50% solution) Proportions Comparative examples AC 100% phenolic resin (standard) Examples (100 parts phenolic resin with parts HEEU) Table 2. Gel time. Minutes at 100ºC Catalyst (as 50% solution) Amounts Comparative Examples AC 100% phenolic resin (standard) Examples (100 parts phenolic resin with parts HEEU) Table 3. Micro Vickers hardness (dry, wet) in GPa Catalyst (as 50% solution) Parts Comparative examples AC 100% phenolic resin (standard) Examples (100 parts phenolic resin parts HEEU)

Comparative example D and examples 7-9

Comparative Example D and Examples 7-9 demonstrated that the standard phenolic phenol-formaldehyde resin modified with the reactive diluent HEEU retained the reactive diluent during and after curing.

Comparison example D

A standard phenolic phenol-formaldehyde resin (i.e., without reactive diluent) was prepared as in Examples A-C, the only differences being the cure time and temperature. Example D was cured at 105ºC for 18 hours, weighed, and heated to 176ºC for a further 20 hours and reweighed. The theoretical and actual weights of the samples are given in Table 4.

Examples 7-9

Three standard modified phenolic resin samples were prepared in accordance with the present invention (Examples 7-9) with various amounts of the reactive diluent HEEU and no alkaline catalyst was added. The samples were cured at 105°C for 18 hours, weighed, then heated to 176°C for an additional 20 hours and reweighed exactly the same as in Example D. The theoretical and actual sample weights of Examples 7-9 are given in Table 4. Table 4 Component Comparative Example D Example Phenolic resin (70 ± 2%) solids HEEU (75% solids) Aliquot Theoretical dry weight Weight after hrs at ºC

Comparative Example E and Examples 10-12 (Nonwoven Abrasives)

Four nonwoven fabrics comprising 126 g/m² of 15 denier, 3.81 cm nylon 6,6 staple fiber (available under the trade designation "Type 101 Bright" from EI Dupont de Nemours & Company, Inc., Wilmington, Delaware) were roll coated with the standard (Example E) and modified blends (Examples 10-12) as shown in Table 5. The resin weight added in each of Examples E and 10-12 was 84 g/m². Water was omitted from the formulations of Examples E and 10-12 because the reactive diluent HEEU had significantly reduced the viscosity of the blends. The coated fabrics of Examples E and 10-12 were dried and cured in a 4.6 meter flow oven continuously at 150ºC and 1.5 meters/minute and then post-cured in a stationary oven for 30 minutes at 135ºC. From the tensile strength data in Table 6, it can be seen that a higher amount of HEEU was detrimental to the tensile strength of the coated fabric of Examples 10 and 11, but there are very useful ranges to work within. Table 5 Component, Parts Comparative Example E Example Isopropanol Standard phenolic resin Red dye mixture Polyamine plasticizer ("EPICURE") Silicone defoamer ("Q2", Dow Chemical Company, Midland, MI) Table 6 Average elongation load at break kg/50.8 mm width Comparative example E Example MD* CD** *MD means the machine direction (warp direction) **CD means the weft direction

Comparative Example F and Examples 13-15 (Nonwoven Abrasives)

Four examples of nonwoven abrasive material were prepared, one with the same standard phenol-formaldehyde resin as used in the previous examples and three with the modified binder prepolymers of the present invention as set forth in Tables 7, 8 and 9. The fibrous mat comprised 13.5 denier, 3.81 cm nylon 6,6 high tensile staple fibers (available from EI Dupont de Nemours & Company, Inc., Wilmington, Delaware under the trade designation "Type P-85"). A prebond coat (Table 8) was applied by a roll coater, dried and cured at 175°C for 10 minutes. A coating in the form of a spray containing Al₂O₃ abrasive grains (Table 9) was then applied by a spray coater, dried and cured at 175°C for 10 minutes. Half of each pre-bond coated fabric was coated with each of the deposit forming mixtures to yield four examples: one consisting entirely of the standard resin (Example F), one containing both the pre-bond and deposit forming in "modified" form (Example 13), and two comprising compositions of the two resin systems (Examples 14, 15) as shown in Tables 8 and 9. The tensile strength of the resulting nonwoven abrasives was measured in both MD and CD and is shown in Table 10. Table 7 Coating step Comparative example F Example Pre-bond Spray coating Standard Modified Table 8. Pre-bond composition Component Standard, proportions Modified, proportions Water Isopropanol Standard phenolic resin Red dye blend Polyamine plasticizer ("EPICURE") Silicone defoamer Table 9. Spray coating composition Component Standard, proportions Modified, proportions Water Phenolic resin Diethylene glycol ethyl ether solvent ("Carbitol") Red dye blend Al₂O₃ (abrasive grains), average grain size 280 microns Table 10. Tensile strength Average elongation load kg/50.8 mm width Comparative example F Example

Comparative examples G-I and examples 16-21 (Formaldehyde emissions)

Comparative Examples G-I and Examples 16-21 were prepared from a phenolic resin having a formaldehyde/phenol ratio of 1.96:1.0, containing no organic solvent and 75% solids. (It was a precursor to the "standard" resin obtained from the manufacturer, Reichold Chemicals, prior to dilution to 70% solids.) These examples further demonstrated that the binder prepolymers of the present invention allow the use of lower amounts of organic solvents in the manufacture of abrasives. In addition, the examples demonstrated the ability of the modified binder prepolymers of the present invention to suppress formaldehyde emission during the manufacture of abrasives. Table 11 gives the composition of Examples G-I and 16-21. For each resin blend of the examples, water tolerance and gel time response were determined. The data are given in Table 12.

To demonstrate the reduction in formaldehyde emissions in the practice of the present invention, 2.0 g samples of each of Comparative Examples G, H and I and Examples 16-21 were placed in an oven at 150°C for 13 minutes. A formaldehyde detector known under the trademark "Interscan" (Model # 1160, available from Interscan Corporation) was used to measure the release of formaldehyde, the results are given in Table 13 and Figures 4-7. The relative formaldehyde release was determined in Examples GI and 16-21 by making copies of the figures, cutting out the areas under the corresponding curves, determining the paper weight of the cutouts of the areas under the corresponding (formaldehyde released in ppm/time) curves, and comparing the weight of each paper cutout to the weight of the cutout for Example G. Table 11 Name of the example Phenolic resin, proportions (75% solids) HEEU, proportions Alkaline catalyst as 50% NaOH, proportions Comparative example Example Table 12 Name of the example Water tolerance, % Gel time, minutes Comparative example Example Table 13 Name of the example Relative formaldehyde emissions in 13 minutes Comparative example Example

Comparative Example J and Examples 22-25 (Bis-Phenol A/Formaldehyde)

The individual resins of Examples J and 22-25 were bis-phenol A/formaldehyde condensates containing 3.5 moles of formaldehyde per mole of bis-phenol A. These blends were not further condensed. The effect of HEEU on the water tolerance of the condensates was studied. The condensate/HEEU blends were very viscous and it was somewhat difficult to measure water tolerance, but the results were very encouraging and demonstrate the breadth of applicability to materials other than standard resole-type phenolic phenol/formaldehyde resins. The compositions are given below in Table 14. In all cases, 100 g of the bis-phenol A material was used. Increasing amounts of HEEU were applied as shown. Table 14 Example HEEU (grams) Water tolerance, % Comparative example J 250 (estimated by extrapolation)

Comparative example K and examples 26-30 (Coated abrasives, grinding performance)

Examples 26-30 and Comparative Example K compared the cutting performance of coated abrasives prepared using the preferred reactive diluent HEEU with the standard phenolic resole resin. The binder prepolymer solutions were prepared using the ingredients listed in Table 15. Table 15. Resin compositions (proportions) Component Control Coating Formation Glue Coating Test Coating Formation Test Glue Coating Phenolic resin, 76% solids* Formaldehyde, 37%* NaOH, 50 wt.%* 2-Ethoxyethanol Water HEEU, 75% solids* Pigment, 50%* * Balance water ** Filler Table 16 Example Coating resin Glue resin Comparative example K Control Test coating formation Test glue

Examples K and 26-30 were prepared with the control coatings and control size coatings as indicated in Table 16. The control phenolic resin used was the same as that used in Examples G-I and 16-21. The backing for Examples K and 26-30 was a woven cotton backing with an X-reinforced four-over-one weave. The backing had a waterproofing treatment and a size treatment on the back. The coatings were applied to achieve a (dry) coating weight of 79 g/m². Grade 80 aluminum oxide abrasive grains were applied to achieve a dry added weight of 250 g/m². The compositions were then cured at 115°C for 30 minutes. The size coats were then applied to give a dry added weight of 113 g/m². The compositions were then cured at 100ºC for 76 minutes. Curing was completed by curing at 100ºC for 10 hours. The resulting coated abrasives were then hand bent and tested using the following procedures:

The products of Examples K and 26-30 were tested by two methods. First, the tests were conducted on a tensile tester known under the trade name "SINTECH". This test was designed to measure the force necessary to remove the backing from the abrasive layer by a 90º peel test, that is, the backing and abrasive layer are at 90º to each other when pulled apart. Test specimens were prepared by attaching a 3" x 12" sample of coated abrasive material, abrasive side down, to a 6" x 3" x 0.3" basswood board with a hot-dissolved isooctyl acrylate/acrylic acid adhesive so that the abrasive layer was held to the basswood board. The long side of each coated abrasive was in the direction of curvature of the backing material. After the adhesive had cooled to ambient temperature, the samples were conditioned at 60% relative humidity for at least 24 hours. After conditioning, the samples were cut to 5 cm width and the backing was separated at one end from the layer comprising the coating, abrasive grains and adhesive layer using the tensile tester. The backing was secured in the upper jaw of the tensile tester and the board was inserted horizontally in the opposite jaw so that the apparatus peeled the backing from the secured abrasive layer at an angle of 90º. The tensile tests were carried out at 2.5 cm/min and the load was recorded continuously. The average force required to remove the backing from the abrasive layer is given in kg per cm width in Table 17. The average values were only slightly less than for Comparative Example K, which was used as a control. was used, and the variations within experiments were considered insignificant.

Grinding performance studies were also conducted using the products of Examples K and 26-30. The grinding test was used as a measure of the ability of the coated abrasives to effectively remove material from the material samples. An endless belt measuring 7.6 cm wide x 335 cm circumference was made from each coated abrasive material of Examples K and 26-30. Each belt was mounted on a belt sander with a toothed (1:1, 1.3 cm) 35.6 cm diameter contact wheel of 60 A durometer. Each belt was driven at a rate of 1950 surface meters per minute (no load) and pressed against a 17.8 cm x 2.5 cm x 5 cm (length x width x height) workpiece with a load of 6.8 kg for one minute periods at a reciprocating speed of 6 meters per minute. The initial and final weight of the workpiece was recorded ten minutes after each one minute interval. To minimize the effects of frictional heat, the workpiece was changed every minute of the test. Each belt was tested with both 4150 malleable steel and 17-4 stainless steel workpieces. The results are shown in Tables 18 and 19. Table 17 Example 90º peeling, average force, kg/cm Comparative example K Table 18 Results of the emery belt tests on 4150 steel (in grams of grinding) Grams of grinding per 1 minute interval Example total grinding Table 19 Results of the emery belt tests on 17-4 stainless steel (in grams of cut) Grams of cut per 1 minute interval Example Total cut

Example 31

Preparation of a coated abrasive using a phenolic resole resin, an ethylenically unsaturated monomer and a reactive diluent and its grinding performance.

A coated abrasive was prepared using an A weight waterproof sandpaper backing available from Kimberly-Clark Corporation, Roswell, Georgia, and using Grade 1200 silicon carbide abrasive grains (JIS standard, average particle size 9.5 micrometers). The coating and size coats having the compositions shown in Table 20 were applied.

The viscosity of the coating (78% solids, after dilution with water) was 225 cps while that of the size resin (60% solids after dilution with "Hi-Sol 10") was 50 cps, the viscosity of each being measured using a Brookfield viscometer, spindle number 2 at 60 rpm and at 25ºC for the coating and at 30ºC for the size resin. In the preparation of the coating, the ingredients were mixed in the order of arrangement in Table 20 and then diluted with water. In the preparation of the size coating, the wetting agent and solvent were thoroughly mixed with the epoxy resin before adding the hardener and "Hi-Sol 10".

For the example, the coating was applied using a roll coater to achieve a weight of 10.5 g/m², then exposed to ultraviolet irradiation using a lamp power of 118 watts/cm and an irradiation rate of 30.5 meters per minute, whereby the coating partially gelled. The silicon carbide abrasive grains were then electrostatically precipitated onto the coating coated paper backing. The partially gelled coating coated abrasive grain coated backing was heated to 115°C for 30 minutes, whereby the coating partially cured. The size coating was then applied over the partially cured coating to achieve a weight of 12.5 g/m² using a roll coater. The structure was then heated to 115ºC for a further 70 minutes, during which the coating and the glue coating were completely cured.

A test of abrasive performance was conducted using a standardized abrasive test apparatus known under the trade name "Slate." The coated abrasive prepared above, after fully cured, was cut into a 4" disk, attached to a foam backing pad with a pressure sensitive adhesive, and mounted on the apparatus. During the test, a workpiece was rotated while being pressed against the stationary coated abrasive.

A test workpiece was weighed at the beginning and after 500 cycles of rotation and the cumulative weight loss in grams of the workpiece was determined. In this case, the workpiece was a 10.2 cm diameter polymethyl methacrylate disk made to imitate a painted surface. The cumulative grinding percentage is given in Table 21.

For comparison, a control was produced with the same abrasive grains and the same adhesive coating.

The control deposit contained 44.8% epoxy resin ("EPON 871"), 22.6% of an 85%/15% solution of the hardener/solvent ("Versacure"/"Hi-Sol 10"), 0.4% wetting agent solution (10% rheology thinner "Modaflow", 90% solvent "Hi-Sol 10") and 32.2% solvent ("Hi-Sol 10"). After 2500 periods of the test apparatus ("Schiefer"), a cumulative cut of only 1.9 g was achieved. Table 20 (Example 31) Composition of the coating formation (wt. %) Composition of the glue coating (wt. %) Phenolic standard resin (43%) Tetraethylene glycol diacrylate (32%) Polyethylene glycol (molecular weight = 600) (20%) Hardener (trade name "Irgacure 651") (1.5%) Wetting agent (trade name "Silwet L-7604) (0.25%) Wetting agent (trade name "Interwet") (0.25%) Reactive thinner HEEU (trade name "UCAR RD-65-2") (3.0%) Epoxy resin (trade name "EPON 828") (35%) Polyamide hardener (trade name "Versacure 125 SC85") (41.2%) Solvent (trade name (20%) "Hi-Sol 10") (23.3%) Wetting agent (10% solution of "Modaflow" in "Hi-Sol 10" solvent) (0.5%) Table 21. Grinding performance Periods Cumulative grinding (g)

Comparative examples L and M and examples 32-37 (More examples of formaldehyde emissions)

To determine the reduction in formaldehyde emissions from the coatable, thermally curable binder prepolymer solutions using reactive diluents such as alkyl substituted 2-amino alcohols, β-ketoalkylamides and nitroalkanes, 2.0 g samples of Compositions L and M and Examples 32-37 as shown in Table 22 were placed in an oven at 150°C for 13 minutes. Using the formaldehyde detector known under the trademark "Interscan" Model #1160, as in Examples GI and 16-21 above, the relative formaldehyde release for the compositions of Examples L and M and 32-37 was determined by adding the areas under the curves at 15 second intervals to obtain the total area under each curve, multiplying this sum by the total elapsed time and dividing by the value obtained for the control. The relative formaldehyde emissions are given in Table 23. Figures 8 and 9 show graphically that increased amounts of 2-amino-2-methyl-1-propanol (AMP, Fig. 8), β-ketobutyramide (BKB, Fig. 9) and nitromethane (NM, Fig. 10) significantly reduced the formaldehyde emission compared to solutions not containing the reactive diluents. Table 22 Example Name Phenolic Resin, Amounts (75% solids)* Reactive Diluent, Alkaline Catalyst (as 50% NaOH), Amounts * the same resin used in Examples GI and 16-21. Table 23 Example designation Relative formaldehyde emissions Comparative example Example

Examples 38-43 and comparative examples N O and P Comparative examples N O and P

Comparative Example N was a micro-thin coated grinding wheel available under the trade designations "Imperial" "Wetordry" 1200 414Q from Minnesota Mining and Manufacturing Company, St. Paul, Minnesota.

Comparative Example O was a coated grinding wheel available under the trade name "Nikken" Grade CC 1200-Cw from Nihonkenshi Company, Ltd., Japan.

Comparative Example P contained coating and sizing resins listed in Table 25 and had a paper backing.

Examples 38-43

Paper-backed abrasives containing Grade 1200 silicon carbide were prepared in the laboratory using blends of the phenolic resole resin and the reactive thinner known under the trade name "Jeffamine" as deposit and sizing resins versus standard epoxy resins. A single mineral layer construction was used for all test batches of Grade 1200 silicon carbide abrasive grains. The batches were compared with Comparative Examples N and O. Three blends of the deposit and sizing resins of the phenolic resole resin/reactive thinner were evaluated. The compositions of the blends are given in Table 24. In preparing the resins in Table 24, some water was added to the phenolic resin prior to adding the reactive thinner and an additional amount of water was added to adjust the solids content. It was not heated externally.

The blends were used to prepare the examples given in Table 25. Comparative Examples D and E were adjusted to the desired percent solids using the solvent known under the trade designation "Aromatic 100". The phenolic resole resins modified by the reactive diluent were adjusted to the desired percent solids using only tap water. All samples were tested using the wet medium slate test on acrylic panels. The results are given in Table 26, along with test data for Comparative Examples A and B. Table 24 Component Test resin A (coating formation) Test resin B (coating formation and glue resin) Test resin C (glue resin) Comparison resin Phenolic resole resin Jeffamine Reactive thinner Jeffamine EDR-148 Reactive thinner Silane Silwet Interwet Water EPON 871 Epoxidhard Versamid 125 Modaflow Aromatic 100 EPON 828 Epoxy resin to 45% Solids or 48% (glue) Table 25 Example of coating adhesive (% solids) Coating weight (g/m²) Mineral Mineral weight (g/m²) Glue adhesive Glue weight (g/m²) Comparison resin Test resin SiC grade Table 26. Cumulative cut (g) Example cut by periods

After After the initial slate cut test, samples from the test and control samples were soaked in water at room temperature for 20 hours and the cut and polish were retested. The results are shown in Table 27. Table 27 Example 500 Period polish (Rtm) 2500 Period grind (g)

Examples 44-47

Examples 44-47 demonstrate the utility of the present invention in making a grinding wheel with a paper backing containing P-400 grade Al₂O₃. The resin compositions are given in Table 28 with the reactive diluent added back after some water was added to the phenolic resin. Grinding wheels 44-47 had the construction described in Table 29. The cumulative slate cut for these examples is given in Table 30. In the examples containing the reactive diluent, a consistently improved cut of the abrasive is evident. Table 28 Component Comparison resin Test resin Epon 828 Epoxy resin Phenolic resole resin (75% solids) Versacure (85% solids in Aromatic 100) Interwet Ethylcellosolve Modaflow Aromatic 100 Water Jeffamine ED600 Silwet L-7604 Interwet to 68% solids Table 29 Example Coating Adhesive (% solids) Coating Weight g/m² Mineral Weight g/m² Glue Adhesive (% solids) Glue Weight g/m² Resin Table 30 Example cut according to periods,

Comparative example Q and example 48

Comparative Example Q and Example 48 illustrate the preparation of a coated abrasive of the invention comprising a phenolic resole resin, an ethylenically unsaturated monomer and a reactive diluent.

A coated abrasive was prepared using an "A" weight paper backing and grade 1200 silicon carbide abrasive grains. Comparative Example Q was prepared using Comparative Resin D (Table 24) for the coating resin. and the comparative resin E (Table 24) for the sizing resin. The deposit formation and sizing resins for Example 48 are given in Table 31. Some water was added to the phenolic resin before the addition of the reactive diluent. It was not heated externally. Table 31 Component Scale Forming Resin for Example 48 Glue Resin Phenolic Resole Resin Irgacure 651 Interwet Jeffamine Silwet L7604 Water to 180 centipoise to 50 centipoise (68% solids) (60% solids)

After the resins reached 25°C, the viscosity was measured using a Brookfield viscometer, spindle number 2 at 60 rpm, for the deposit forming resin at 25°C and for the size resin at 30°C. The various coating weights are given in Table 32. The deposit was then coated onto the paper backing. The structure for Example 48 was exposed to a 300 watt/inch UV lamp for 0.5 second to partially cure. Silicon carbide abrasive grains were then electrostatically coated onto the deposits for Example 48 and Comparative Example Q and the structures were heated at 115°C for 30 minutes to partially cure the deposits. The size coat was then coated onto each structure and the resulting compositions heated at 115°C for an additional 70 minutes to complete cure. The resulting coated abrasives were tested for cumulative cut using the wet slate test. The results showing the comparison of this example with Comparative Example N and Comparative Example O are given in Table 33. Table 32 Example Coating weight g/m² Mineral weight g/m² Glue weight g/m² Comparative example Table 33. Slate cut example Cumulative cut at 500 periods, g Comparative example N

This work provides evidence that abrasives made with coatable, thermally curable binder prepolymer solutions have as good or better performance, with reduced formaldehyde emissions, than previously known abrasives.

Claims (29)

1. Coatable, thermally curable binder prepolymer solution, characterized in that it is a combination of: (a) a 30-95% solids solution of a thermally curable resin having multiple pendant methylol groups, the balance of the solution being water; and (b) a reactive diluent, wherein the thermally curable resin is the reaction product of a compound that is not an aldehyde and an aldehyde, the product that is not an aldehyde is selected from the group consisting of ureas and phenols, and wherein the reactive diluent has at least one functional group that is independently reactive with the pendent methylol groups or with the aldehyde, and wherein the reactive diluent is selected from the group consisting of A) Compounds selected from the group consisting of compounds of the general formula and mixtures thereof, wherein X = O or S and Y = -NR³R⁴ or -OR⁵, with the proviso that if X = S, Y = -NR³R⁴, each of R¹, R², R³, R⁴ and R⁵ is a monovalent radical selected from the group consisting of a hydrogen atom, alkyl radicals having 1 to 10 carbon atoms, hydroxyalkyl radicals having 2 to 4 carbon atoms and one or more hydroxy groups, and hydroxypolyalkyleneoxy radicals having one or more hydroxy groups, and with the provisos that: (i) the compound contains at least one -NH- and one -OH group or at least two -OH groups or at least two -NH- groups; (ii) R¹ and R² or R¹ and R³ may be bonded together to form a ring structure; and (iii) R¹, R², R³, R⁴ and R⁵ cannot simultaneously each represent a hydrogen atom; B) compounds having a molecular weight lower than 300 and selected from the group consisting of alkyl-substituted 2-alnino alcohols, β-ketoalkylamides and nitroalkanes; C) poly(oxyalkylene)amines having a molecular weight in the range of 90 to 300; and D) Poly(oxyalkylene)ureido compounds having a molecular weight in the range from 90 to 1000. 2. The solution of claim 1, further characterized in that the compound other than an aldehyde is phenol and the aldehyde is formaldehyde. 3. Solution according to claim 1, further characterized in that the thermally curable resin is selected from the group consisting of phenolic resins, urea-aldehyde resins and mixtures thereof. 4. The solution of claim 3, further characterized in that the thermally curable resin is a phenolic resin selected from the group consisting of novolak, resole and resolized novolak resins. 5. The solution of claim 1, further characterized in that at least one functional group reactive with the pendant methylol groups is a -NH- group. 6. Solution according to one of claims 1 to 5, further characterized in that the reactive diluent has a molecular weight of at most 600. 7. Solution according to claim 6, further characterized in that the reactive diluent has a molecular weight of at most 300. 8. Solution according to claim 4, further characterized in that the phenolic resin is a resole. 9. Solution according to one of claims 1 to 8, further characterized in that water is contained in a sufficient amount so that the resulting solution has a permanently milky appearance. 10. Solution according to one of claims 1 to 9, further characterized in that the thermally curable resin and the reactive diluent are present in a weight ratio in the range of 1:1 to 100:1. 11. Solution according to one of claims 1 to 9, further characterized in that the thermally curable resin and the reactive diluent are present in a weight ratio in the range of 2:1 to 100:1. 12. Solution according to one of claims 1 to 11, further characterized in that the solution also contains abrasive grains. 13. Solution according to one of claims 1 to 12, further characterized in that X is O, Y = -NR³R⁴, R¹ is the 2-hydroxyethyl group, R² and R³ are bonded to one another to form an ethylene bridge, and R⁴ is a hydrogen atom. 14. A solution according to any one of claims 1 to 12, further characterized in that X is O, Y=-NR³R⁴, R¹ and R³ each represent a hydrogen atom, R² is a butyl group and R⁴ represents a hydroxyethyl group. 15. A solution according to any one of claims 1 to 12, further characterized in that X is O, Y is -NR³R⁴, R¹ and R³ are each hydrogen, R² is ethyl and R⁴ is butyl. 16. Solution according to one of claims 1 to 12, further characterized in that the reactive diluent is a poly(oxyalkylene)amine selected from the group consisting of compounds of the general formula where R6 is an alkyl radical having 1 to 4 carbon atoms and n and m represent integers in the range from 0 to 20. 17. Solution according to one of claims 1 to 12, further characterized in that the reactive diluent is a poly(oxyalkylene)amine selected from the group consisting of compounds of the general formula where x is an integer in the range 2 to 20. 18. Solution according to one of claims 1 to 12, further characterized in that the reactive diluent is a poly(oxyalkylene)amine selected from the group consisting of compounds of the general formula where a, b and c are integers, the sum of a plus c is in the range 1 to 5 and b is in the range 0 to 20. 19. Solution according to one of claims 1 to 12, further characterized in that the reactive diluent is a poly(oxyalkylene)amine selected from the group consisting of compounds of the general formula where m, n and o are integers greater than zero, the sum of m, n and o is in the range from 5 to 30, and where A is a triol initiator. 20. A cured form of a solution according to any one of claims 1 to 19. 21. An abrasive which contains a plurality of abrasive grains dispersed and firmly adhered in a binder, the binder being produced by curing the binder prepolymer solution according to any one of claims 1 to 11 and 13 to 19, wherein if the reactive diluent is a poly(oxyalkylene)amine, the molecular weight of the poly(oxyalkylene)amine is in the range of 90 to 1000, with the proviso that if the abrasive is a nonwoven abrasive, the molecular weight of the poly(oxyalkylene)amine is less than 300. 22. An abrasive according to claim 21, further characterized in that the abrasive grains are selected from flint, garnet, aluminum oxide, alumina-zirconia, cutting diamond, silicon carbide, cubic boron nitride, silicon nitride and mixtures thereof. 23. Abrasive according to claim 21 or 22, further characterized in that the coatable, thermally curable binder prepolymer solution comprises a thermosetting catalyst. 24. An abrasive according to claim 23, further characterized in that the thermosetting catalyst is benzoyl peroxide. 25. An abrasive according to any one of claims 21 to 24, further characterized in that the binder further comprises a component selected from the group consisting of fillers, coupling agents, surfactants, wetting agents, plasticizers, fibers, dyes, pigments, grinding aids and mixtures thereof. 26. Abrasive according to one of claims 21 to 25, further characterized in that it is a bonded abrasive. 27. An abrasive according to any one of claims 21 to 25, further characterized in that it is a non-woven abrasive. 28. Abrasive according to one of claims 21 to 25, further characterized in that it is a coated abrasive. 29. An abrasive according to any one of claims 21 to 28, further characterized in that the coatable, thermally curable binder prepolymer solution includes an ethylenically unsaturated monomer.